Prevent user from changing from address.

[abckdc]

I am new to this filed and have been tasked upon to disable our mail users from sending mail changing their from address via email client (outlook and thunderbird).
The zimbraAllowAnyFromAddress is disabled, I have also disabled persona features, and have also done Enforcing a match between the FROM address and the sasl username
but users can still send email on behalf of someone from mail client(outlook and zimbra). I could not find solution to the problem please help!!!
zimbra version --8.8
steps followed from articles:
https://wiki.zimbra.com/wiki/Prevent_Se ... meone_Else
https://wiki.zimbra.com/wiki/Enforcing_ ... l_username